Process for preparing cultch for mollusca

ABSTRACT

This application describes a process for the production of a growth medium or cultch for mollusca, particularly oysters, comprising contacting preformed cultch made from coal ash wastes with larvae of the mollusca and permitting the larvae to settle thereupon.

This application is a division of our copending application Ser. No.07/122,309, filed 11/18/87, now U.S. Pat. No. 4,844,015.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to, and has as its principal object provision of,a novel cultch, or growth medium, for oysters or other molluscs madefrom the wastes left by burning coal in bulk as in power plants.

2. Prior Art

Artificial oyster cultches have been made from various materials. Clarket al, U.S. Pat. No. 3,552,357 (1971),for example, shows use ofhydraulic cement, lime, an antislime lubricant, gypsum, and afiber-binding material. So far, as is known, however, cultch has notbeen made from coal wastes.

THE DRAWINGS

The invention will be understood in physical aspect from the drawings,in which:

FIG. 1 is a pictorial view of a flat irregularly shaped object with twosurfaces, 10 and 11, perferably rough, usable as cultch;

FIG. 2 is a pictorial view of a disk with surfaces 10 and 11 also usableas cultch;

FIG. 3 is a pictorial view of the preferred cultch in the form, andapproximately the weight, of a natural oyster shell with a concavesurface 12, preferred by oyster spat, and a convex surface 13; and

FIG. 4 is a cross-sectional and side-elevational view along line 4--4 ofembodiment shown in FIG. 3.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, cultch is made in a desiredshape from wastes from the combustion of coal. These wastes occur inthree types: flue gas desulfurization sludge (FGD), fly ash (FA), andbottom ash (BA). A large volume of flue gas desulphurization sludge, awaste material composed primarily of calcium sulfate and calciumsulfite, results from the use of desulfurization scrubbers in coal-firedpower plants. Fly ask is a dust which rises and is filtered out of coalcombustion gases. Bottom ash is the gravelly residue left on the floorof the furnace. Lime kiln dust (LKD), a by-product of lime processing,or cement can also be used in the mixtures up to about 20% by weight.

Three mixtures, all of materials from commercial power plants (exceptLKD), were tested as cultch, and concrete alone (Mix 4) and naturaloyster shells (Mix 5) were used as controls. The three novel mixes were:

Mix 1--FA, FGD and high calcium quicklime at a ratio of 58:38:4;

Mix 2--FA and LKD at a ratio of 85:15; and

Mix 3--BA, FA, and LKD at a ratio of 54:28:18.

The necessity for binders depends on the chemical composition of variousashes. Some have a sufficiently high calcium and magnesium content as tobe self cementing. In any case, about 10% cement will provide sufficientbinding. Compaction will aid in the cementing process but may notsubstitute for binders in lower calcium/magnesium ashes.

To prepare the mixtures, the materials are merely mixed and allowed toset as with concrete. Shaping in the form of oyster shells can be bymolding before setting takes place.

Analysis of experimental data such as that given below indicates thatall ratios of coal ash are suitable for making osyter cultch but thatMix 3, i.e., a mix containing both fly ash and bottom ash as well as upto about 20% of lime kiln dust, is preferred by the oysters, theresponse being approximately equal to that of the natural oyster shellcontrol (Mix 5).

Use of coal ash wastes for cultch provides at least a partial answer totwo problems. It provides a cheap source of cultch itself, important inoyster-growing areas such as the Chesapeake Bay region. Furthermore, itprovides a method of disposal for coal wastes, an environmental problemfor the electric power industry. Moreover, in rate of growth of oysters,the present cultch is superior to the rate on natural oyster shells.

Coal ash-waste cultch also has certain advantages over concrete cultch.For example, dark coloration of the coal-waste cultch is attractive tooyster larvae because they are negatively phototropic, i.e., areattracted to dark places. More important, probably, is the fact thatoyster larvae prefer rough/pitted surfaces. Mix 3 is best here becauseof the granular nature of the bottom ash. Finally, oyster larvae areprobably also attracted to ash because of the high calcium and magnesiumcontent of the material used by the oyster in building its shell.

EXAMPLE

As example illustrating the invention is as follows:

Larvae were produced in the laboratory utilizing the methodologydescribed by Ewart (Support Activities--Hatchery, pp. 87-97, in E. T.Bolton (Ed.) Intensive Marine Bivalve Cultivation in a ControlledRecirculating Seawater Prototype System DEL-SG-07-82). When larvaedeveloped eyespots (i.e., generally ready to set in 24-48 hours), theywere transferred at a density of 1.5 larvae/ml to a setting/growout tankcontaining various substrata. In total, 1,200,000 larvae were equallydivided between two 400L tanks with dimensions of 94 cm long×75 cm wide×64 cm deep.

Five different substrata were available for spat set, as noted above.Mixes 1-5 were used as disks 15.2 cm in diameter by 5.1 cm thick. Mix 5consisted of eight to ten whole oyster shells stacked on top of eachother so as to approximate, as closely as possible, the dimensions ofMixes 1-4.

To determine whether substratum age influences setting, Mixes 1-4 weresoaked in seawater for 39 days, eight days, or zero days prior toaddition of larvae. Individual disks were assigned to an aging group byrandom sampling. Each of these three aging conditions was examined inquadruplicate. All five substrata were encircled with a 1.75 inch thicksection of polyvinyl chloride pipe and secured with nylon wire ties toplastic trays. The trays allowed exposure of both sides of the substratato larvae. Each of the two tanks initially contained 12 trays,vertically positioned, for a total of 24 trays. Various substrate typeswere arranged in sequential fashion so that position effects werenormalized for each of the four replicate trays.

Starting one week after larvae had been added to the tank, the height ofoysters, taken as the distance from hinge to bill, was measured to thenearest millimeter. Oysters growing on both sides of mixes 1-5 weremeasured at two-week intervals for 11 weeks, and four-week intervalshereafter for 16 additional weeks. The total number of oysters presenton both sides of each substratum was tallied concurrently.

Approximately three weeks after setting, when an average size of 4-6 mmin height was obtained, one-half of the oysters were transferred to thefield. Trays were suspended in a modular form from a raft floating atthe mouth of the Broadkill River (Delaware). Laboratory oysters weremaintained for six months after setting while the field portion of theexperiment was run for seven weeks postset. Extensive fouling made itnecessary to terminate the field component of the study at that time asthe tremendous tunicate and bryozoan population threatened to smotherunderlying oysters.

Young oysters were maintained in the laboratory in seawater at 30% and23°-25° C. Water was filtered in order to provide a relativelyhomogeneous environment. Tanks were constantly aerated so that dissolvedoxygen concentration was around 6.50 mg/l. This value is comparable tothe 695 mg/l oxygen solubility value for saturated water at 25° C. and30%. Tank water was changed two to three times a week. Diet consisted ofcombinations of four algal species: Isochrysis galbana, Thalossiosirapseudonana, Chaetoceros gracile, and Va-52, a small green flagellate ofunidentified species. The amount of algae the oysters received each dayranged from 1×10¹⁰ to 11×10¹⁰ cells per tank, depending on theavailability of algae at any given time. Based on the presence of afaint tinge of algae in the tank 24 hours after feeding, 2-3×10¹¹ cellsper tank was initially necessary for growing oysters to feed in excess.

At the termination of laboratory and field experiments, oysters weremeasured, scraped free of substrata, pooled by aging and growoutconditions with oysters grown on the same mix, and placed in plasticbags for freezing. Upon thawing, the entire visceral mass, includingadductor muscle, was removed with a plastic utensil and weighed. Whenpossible, enough oysters were opened to obtain 10-12 g of wet tissue inorder to have a 1-2 g dry weight sample for determination of metalconcentration. The remaining oysters were left intact and wet weightobtained for later determinations of condition index. Where there werenot enough oysters in a pooled quadruplicate sample to obtain the 10-12g wet-tissue weight, tissue was removed from all but two or threeoysters. This tissue was then further pooled with other underweightsamples of similar aging and/or growout conditions. The two or threeremaining oysters were used in condition index analyses as before. Thetwo condition parameters analyzed were the ratio:

    (dry soft tissue (g) / dry shell weight (g))×1000

and percent organic content. The ash weight was converted to percentorganics by the formula:

    (total dry weight (g)-total ash weight(g)/total dry weight(g))×100.

From analysis of the data obtained experimentally, it was concludedthat:

1. There is a setting preference by oyster larvae for a coal wastemixture of bottom ash and lime kiln dust approximately equaling that foroyster shell, the natural cultch material.

2. Significant mortality occurred only on Mix 2 in laboratory cultures.

3. Oysters growing in control Mix 5 (oyster shell) had a significantlyslower rate of growth than those on the other substrata, and rate ofgrowth was significantly greater for oysters grown in the field.

Having described our invention, we claim:
 1. A process for preparing acultch for mollusca carrying line mollusca which comprises contacting apreformed cultch made from coal waste mixed with not more than about 20%by weight of binder material with larvae of the mollusca and permittingthe larvae to settle thereupon.
 2. The process of claim 1 wherein themollusca are oysters.
 3. The process of claim 2 wherein the cultch isformed from fly ash, flue gas, disulfurization sludge and quicklime. 4.The process of claim 2 wherein the cultch is formed from fly ash andlime kiln dust.
 5. The process of claim 2 wherein the cultch is formedfrom bottom ash, flue ash, and lime kiln dust.
 6. The process of claim 1wherein the cultch is in the form of a disk.
 7. The process of claim 1wherein the cultch is in the form of an oyster shell.